Tissue specimens for histological examinations are prepared by means of multiple chemical treatments and a final embedding of the specimen in paraffin. In the chemical treatment, the specimen is first fixed with a suitable chemical liquid, and then the water contained in the specimen is removed and is then replaced with stabilizers, dyes, and the like. Lastly, the specimen is embedded in paraffin or wax. The result is that a paraffin block can be held in stable fashion in a receptacle of a microtome for the cutting of individual thin tissue sections. So-called tissue infiltration apparatuses or automatic embedders, which automatically transport the specimens into the various treatment phases, were developed for the various method steps proceeding in succession.
A specimen can be tissue or body fluids from humans or various species of animals, plants, or insects and will vary in size from small biopsies to whole organs to whole bodies. Specimens are processed with the objective that a diagnosis will be rendered after thin sections of the specimen are stained and examined microscopically to determine cellular morphology, chemical composition and the function of normal and abnormal tissue. These specimens are each introduced into a cassette, in which they are transported through the individual treatment steps. Reference is made, purely by way of example, to DE 103 42 264 A1 which describes, inter alia, such a cassette. These specimens, or thin tissue sections thereof, are ultimately intended to be conveyed for histological examination. For this, a pathologist views, with the aid of a microscope, a specimen section prepared with a microtome and placed onto a specimen slide; the specimen section can be stained with a staining method and provided with a coverslip.
The transport apparatus of the tissue infiltration apparatus is intended in particular to make it possible to transport at least two transport baskets simultaneously in the tissue infiltration apparatus, or to transport two transport baskets, present simultaneously in the tissue infiltration apparatus, in succession with a time offset. As a rule, a transport basket is brought to a liquid container and into it using the transport apparatus. With the transport apparatus the transport basket is then, usually at a later point in time, moved out of a liquid container and away from the liquid container.
An “execution sequence” or “processing order” for purposes of the present invention is to be understood in particular to mean that an order in which a transport basket having cassettes passes through the liquid containers provided in the tissue infiltration apparatus is predefined or can be predefined (for example by an operator of the tissue infiltration apparatus). A liquid container can also be construed here as a processing station at which the cassettes (and therefore specimens) present in a transport basket are introduced into the liquid provided in the liquid container, with the result that the liquid acts on the specimens. In this context, the term “pass through” is to be understood for purposes of the present invention, in particular, as follows:                delivery of a transport basket, having cassettes and accordingly having specimens, from an input station, at which a transport basket is transferred to the tissue infiltration apparatus, to and into the first liquid container in the execution sequence;        removal from the liquid container after a definable contact time;        delivery of a transport basket to and into the next liquid container, etc.; and lastly        delivery to an output or transfer station at which a processed transport basket can be outputted or removed from the tissue infiltration apparatus.        
DE 196 47 662 C1, for example, discloses a tissue infiltration apparatus in which a plurality of liquid containers are arranged in circular fashion. One, and in some circumstances also multiple, transport baskets can be transferred successively in time-offset fashion to this tissue infiltration apparatus. These baskets are conveyed by the transport apparatus provided therein, in a predefined rotation direction, from one liquid container to the next; the transport apparatus provided therein is configured in such a way that in the context of a transport operation, all the transport baskets present in the tissue infiltration apparatus are delivered to the respective next liquid container. One complete pass by a transport basket can require one to several hours. Fully automated tissue infiltration apparatuses can, when appropriately loaded, be operated automatically overnight. As soon as one transport basket is transferred to the tissue infiltration apparatus, a further transport basket can be transferred to the tissue infiltration apparatus, but it is transported and thus processed sequentially, through the individual stations or liquid containers of the tissue infiltration apparatus, in the same execution sequence as the transport basket already present in the tissue infiltration apparatus. If the specimens present in a transport basket need to be processed in particularly urgent fashion, this is not readily possible with the tissue infiltration apparatus known from DE 196 47 662 C1, since transport baskets already present in the tissue infiltration apparatus cannot readily be removed prior to a complete pass through the tissue infiltration apparatus.
This problem is addressed in DE 101 63 488 A1, which provides a tissue infiltration apparatus that comprises an additional liquid container having a smaller fill volume than the first treatment chamber. Multiple transport baskets are processed in the first treatment chamber. In the additional liquid container, a transport basket can be subjected to urgent processing. In this context, the liquid necessary for the particular processing step is respectively introduced into said liquid container and, after a predefined contact time, drained again. This enables a transport basket to be subjected to an urgent tissue infiltration, but it is also necessary, once the liquid container has been drained, firstly to clean it before it can be filled with another liquid. This in turn is complex, and requires complex controlling of the filling and draining operations and of the liquid container and the first treatment chamber. Cleaning reagents must additionally be used, thus increasing operating costs for the tissue infiltration apparatus.